Maturation of Energy Metabolism in the Lamb: Changes in Myosin ATPase and Creatine Kinase Activities

Abstract

Studies have been carried out to assess maturation of myofibrillar and mitochondrial proteins in fetal (1 13 to 140 days gestation), neonatal (-10 min to 21 days postpartum), and adult sheep hearts.Ca++-activated myosin ATPase activity was-20% lower in fetal than in adult left ventricular myocardium (1.13 + 0.06, n = 12, versus 1.36 .+ 0.07, n = 9, pmoles PI per g protein per sec; P < 0.025). In fetal and neonatal hearts (but not in adult hearts), myosin ATPase activity was slightly higher (-14%; P < 0.001) in right ventricular tissue than in left ventricular tissue. In contrast to these small changes in myosin ATPase activity, large changes indicative of maturation of energy metabolism occurred in the creatine kinase system: between 115 days gestation and 21 days postpartum, total creating kinase activity increased nearly &fold (0.2 to 1.6 IU/mg cardiac mass), the MM-creatine kinase isozyme increased 7-fold (0.2 to 1.5 IU/mg wet weight), and mitochondrial creatine kinase increased more than 25-fold (< 0.01 to 0.27 IU/ mg wet weight). The total creatine pool, but not the ATP pool, increased (from-6 to-15 nmoles/g tissue). Neither the concentration nor isozyme distribution of lactate dehydrogenase, a glycolytic enzyme, changed during this 7-wk period of development. Speculation and lactate dehydrogenase isozyme compositions. The results suggest that an age dependency exists in the enzymes important in regulating energy production and utilization. MATERIALS AND METHODS Myocardial tissue was obtained after rapid cardiectomy from 17 fetal sheep ranging in age from 113 to 140 days gestation, 22 newborn lambs ranging in age from 30 min to 21 days, and 13 adult (mother) sheep. ENZYME ANALYSES Myosin. Myosin (ATPase, EC 3.6.1.3) was isolated from 10 to 20 g tissue using the method of Katz (21). In all cases, the yield was-8 mg/g tissue. Calcium-activated myosin ATPase activity was assayed at 25OC in 0.1 M Tris (pH 8) containing 0.6 M KCI. 10 mM calcium, and 3.1 mM MgATP. The reaction was stopped by adding an aliquot of 70% perchloric acid. The liberated inorganic phosphate was measured using the Fiske-Subbarrow method (9). Myosin ATPase activity was calculated as moles of inorganic phosphate produced per protein per sec. The purity of the myosin preparations was assessed using sodium dodecyl sulfatepolyacrylamide gel electrophoresis (5% cross-linked) as previously described (15). We speculate that changes in biochemical composition of en-Separate tissue samples were used for analyses of creatine kinase ergy-utilizing and-producing proteins, coupled with alterations in and lactic dehydrogenase activities. Samples were homogenized the structure and cellular distribution of mitochondria and myofi-in 0.1 M potassium phosphate buffer (pH 7.4) with I mM EDTA brils, contribute to the changes in mechanical performance char-and 1 mM /I-mercaptoethanol, and allowed to incubate for I hr to acteristic of the maturing heart. release mitochondria1 isozyme as described by Jacobus and Lehninger (18). Creatine kinase activity (ATP; creat...

Milrinone Effects in the Isolated Immature Rabbit Heart

“…tant differences between immature and adult myocardium, which might help explain agerelated changes in contractility. These devel opmental differences include: lower intracel lular calcium concentration [15], decreased adenylate cyclase activity [16], decreased myofibrillar content [17], decreased myofi brillar ATPase activity [18], immaturity and decreased quantity of sarcoplasmic reticulum [19] , and differences in myosin isoenzymes [20] , For isoproterenol, the mechanism of action is mediated by the ß-receptor. This receptor has been noted to be reduced in num ber in the immature heart [21], Although these developmental features may explain the decreased sensitivity of newborns to ino tropic stimulation, it is pertinent to note that the contractile proteins from immature and adult myocardium appear to be equally sensi tive to calcium stimulation [22], This latter finding suggests that the failure of the stan dard inotropic drugs in the immature heart is due to a relative inability to increase intracel lular calcium.…”

Antenatal Glucocorticoid Therapy Accelerates ATP Production With Creatine Kinase Increase in the Growth-Enhanced Fetal Rat Heart

“…40, 41 Ingwall et al reported that activity of CK-M and Mi-CK was significantly increased in the normally developing fetal heart, suggesting that maturation of the CK enzyme system is required for energy production and utilization by the aerobic pathway. 32 In our results, there were no differences in the ATP levels of the control and DEX groups of 21-day fetal hearts. Because ATP is synthesized anaerobically (ie, glycolysis) without CK system utilization in the 21-day fetal heart, antenatal DEX administration would not affect ATP production.…”

“…[28][29][30][31][32] Another investigation reported that GC administration enhances the transcription of the CK gene and that this is reflected in functional upregulation of CK. 33 Thus, DEX exerts direct transcriptional effects on the CK gene in fetal hearts.…”

Effects of Angiotensin-converting Enzyme Inhibition on Changes in Left Ventricular Myocardial Creatine Kinase System After Myocardial Infarction: Their Relation to Ventricular Remodeling and Function

“…Relation of LV myocardial CK system to LV dysfunction and remodeling: It is generally recognized that there are increases in total CK activity and the mitochondrial CK fraction and decreases in fetal isoenzyme MB-and BB-CK fractions during the development of fetal to adult normal hearts. 23) A number of investigators reported changes in the cardiac CK system in chronic heart failure after experimental MI in rats, usually at 8 weeks after coronary ligation. 5,6,8,[10][11][12] These included reductions in total CK and mitochondrial CK activities and decreased total CR levels, as shown at 12 weeks after MI in the present study.…”